1. Field of the Invention
This invention relates in general to fuel cell structures and assemblies, and method of making the same.
2. Description of the Art
U.S. Pat. Nos. 5,916,514; 5,928,808; 5,989,300; 6,004,691; 6,338,913; 6,399,232; 6,403,248; 6,403,517; 6,444,339; and 6,495,281 describe microfibrous electrochemical cell structures that each contain an inner current collector, an inner electrocatalyst layer, a hollow fibrous membrane separator with electrolyte medium therein, an outer electrocatalyst layer, and an outer current collector. Specifically, both the inner and outer current collects are made of metal fibers and are disposed respectively on the inner and the outer surface of the hollow fibrous membrane separator.
Since such metal-fiber-formed current collectors are directly exposed to the harsh electrochemical environment near the membrane separator surfaces, they are especially susceptible to corrosion. Corrosion of the current collectors can result in ionic contamination of the polymer membrane electrolyte and reduction in ionic conductivity of the cell for transport of protons. In severe cases, electrical disconnection may occur within individual cells or between adjacent cells that are connected together in series or in parallel, which disconnection shortens the useful life of such microfibrous electrochemical cells and reduces the power density of electrochemical assemblies comprising same.
It is accordingly an object of the present invention to provide corrosion-resistant current collectors for prolonging the useful life and enhancing the reliability of such microfibrous electrochemical cells or assemblies comprising same.
Further, for fuel cell applications, the hollow fibrous membrane separator must further provide an inner fluid passage at its bore side, for passing a fuel- or oxidant-containing fluid therethrough. Such inner fluid passage can be easily blocked upon deformation of the hollow fibrous membrane separator, which will in turn reduce the power output of the electrochemical cells. The need for providing and maintaining such inner fluid passage increases the manufacturing costs of the microfibrous fuel cells.
It is therefore another object of the present invention to provide microfibrous fuel cells with inner fluid passage(s) that is easy to produce and blockage-resistant.
Furthermore, for fuel cell applications, the electrical contact generated between the surface of the catalyst and the current collector plays a significant role in the performance of the fuel cell. In general the higher the contact surface area, the lower the contact resistance in the cell, which translates into higher and more efficient power generation.
It is therefore another object of this invention to provide a microfibrous fuel cell with excellent contact between the catalyst layer and the current collector at the bore side of the cell.
Other objects of the present invention will be more fully apparent from the ensuing disclosure and appended claims.